SCIENCE SAYS:

The engines, appliances and electronic devices we use release heat during operation. For instance, think about a laptop computer, which can get uncomfortably warm if you rest it on your legs for too long. That heat is often called “waste heat” because it escapes without being put to good use. So, given how many machines and devices we use — particularly in rich, industrialized countries — could waste heat be warming the planet? Not really. Waste heat is currently responsible for about 100 times less global warming than carbon dioxide and other greenhouse gases. In other words, it’s not a big problem. Not like the 35 billion tons of carbon pollution we put into the air every year when we burn dirty energy like oil and coal.

Whenever we turn on an appliance, or our car, or anything that uses gas or electricity, we generate heat. You can feel some of that heat when you place your laptop on your lap, or when you touch the hood of your car after you've driven somewhere. Where does that heat go? It goes into the atmosphere.

One question many people have is how does this extra heat contribute to global warming. It is a good question, and one easy to answer. In short, the answer is … it doesn’t.

How do we know? Well, we can easily calculate how much energy is used worldwide. Information is available at sources like this one (PDF). Virtually all the energy we use is converted into heat. But when we burn fossil fuels like coal, we also increase the concentration of greenhouse gases in the atmosphere. And those gases trap heat, making the planet steadily warmer.

By doubling the concentration of carbon dioxide in the atmosphere, we will increase Earth’s heat balance by approximately 1,900,000,000,000,000 watts. That is more than 100 times the total amount of heat from all sources of energy around the Earth. So, it is true that there is heat generated from motors, iPhones, computers, etc. But, this heat is negligible compared to the extra energy we get from heat recycled back to Earth by carbon dioxide and other greenhouse gases.